Never done any API/HTTP stuff with lambda, but I've built many ETL pipelines using it.

A few years ago we tried the Kinesis -> Lambda thing, but it failed during a large traffic event. This was due to the way the Kinesis poller works, and was made worse by the fact that we had two lambdas running off the same Kinesis stream.

The main issue was you can't control the Kinesis poller - meaning we ran into resource contention during this high traffic event and the iterator age fell behind quite drastically. So we abandoned it in favour of EMR + Flink + Apache Beam.

Other then that though, the S3 -> Lambda stuff works perfectly, and has been running for 3+ years with no issues.